This invention is related to a method for flame hardening a workpiece that is a vibrated to remove stresses tending to warp the workpiece.
Components of a variety of machines require certain surfaces that are both long wearing and held to close dimensional specifications. Such surfaces may be produced by a variety of techniques, for example, by flame-hardening. However, in making certain types of workpieces such as elongated way beds, some manufacturing steps such as tempering, machining, straightening or flame-hardening step, create internal stresses that gradually warp the workpiece. Warping is undesirable.
Workpieces are measured to determine any dimensional variations from design specifications, usually noted on a blue print. They are conventionally either straightened in a press, or perhaps, machined to remove such dimensional variations. These methods are unsatisfactory because the workpiece still may tend to warp over a period of time because of stresses built into the workpiece. Sometimes the parts are tempered or treated by heat, to obtain a hard surface, but this is also undesirable because the heat may change the metallurgical structure of the workpiece.
Some vibration techniques are known in the art for removing stress from an elongated workpiece. For example, U.S. Pat. No. 3,999,276 which was issued Dec. 28, 1976 to Robert M. Brown, Melvin E. Byrne and George H. Maxwell discloses a method for raising the temperature of a railroad rail to the mean ambient temperature of the locality where the rail is being laid, and then imparting vibrations to the rail to relieve any stress or caused by the temperature change.
U.S. Pat. No. 4,001,053 which was issued Jan. 4, 1977 to Taro Igisu discloses a method for removing residual stress from a metal workpiece by a percussion vibration treatment.
U.S. Pat. No. 4,968,359 which was issued Nov. 6, 1990 to August G. Hebel, Jr., and August G. Hebel, III; U.S. Pat. No. 4,381,673 which was issued May 3, 1983 to Bruce Klauba and Roger Titone; and U.S. Pat. No. 5,035,142 which was issued Jul. 30, 1991 to Alexander I. Dryga, Nikolai A. Zadorozhny, Mikhail A. Kuzmin and Pavel M. Libman disclose various methods for stress-relieving metal parts by applying a vibrating load in frequencies determined by the harmonic vibration modes of the workpiece.
Some vibration systems for stress-relieving metal parts depend upon locating the resonant frequency of the part and then inducing vibratory forces at a frequency below resonance. Since the resonant frequency sometimes shift, it is then necessary to periodically relocate the resonant frequency and stress-relieve the part until the resonant curve stabilizes, indicating that the stresses have been relieved.